Wave transmission network



i Fig.- 2's a'schemati'c- Patented Aug. 21, 1934 Application October 21, 1932,-Serial No.'638,95 1= h This invention relates to wave 'transmis'sion networks; and more particularly to'the use of mutually coupled inductances in such networks. Thetprincipal object is to reduce the number of coils required in a transmission network.

Another object is to reduce the weight and sizejof transmission networks.-

A further object is toreduce the manufacturing cost of transmission networks. 7

- g i In effectingf'these objects, use is made of the mutual induction existing between two coil wind ings wound on the same core. It-has been shown in the article "Mutual Inductance in Wave Filters with' an Introduction on Filter Design 5 by K. I'S..Johnson and 'r. E. Shea in theBell System Technical Journal, January 1925 that a coupled two-winding coil or transformer is electrically equivalent to a star or T-network of three inductances. If the two'c'oil winding s'are 5720 connected series opposing the equivalent T-net- :30 T will become z'ero and thus disappear. The

remaining two arms may be designed to have any desired values of inductance. :In this way th'ere is provided a coil consisting of two windingswhich may be placed on a common core an potted in the same case but" which willsupply the equivalentof two electricallyseparate inductances. When coils of this'typea're usedin transmission networks such, for example, I as 7 wave filters, there is effected a saving'of atl'e'ast half of the separate coils required by the usual method of design, since one-coil is made totake the placeof two or more.

The'nature of the invention and'themann'er of its application will be more fully understood connection with the accompanyingfdrawing," of whichf' j Figsgland 4 show" two embodiments or the invention in wavefilters'; i dia r m; to which ref erence is made in explaining the invention: and 7 Figs, 3 and?) represent circuit's'which are electrically equivalent to those shown, respectively, i Figs, '1 and I One means of carrying out the inventive idea from gthe following detailed description" taken in.

in Claims. (olli 178544) in practice is illustrated in connection with the wave filter shown in Fig. 1. The figureillus trates schematically a filter section having a pair of input terminals and a pair of output terminals, adapted to beconnected between two sections of a circuit. A pair offequal condensers C1 are'connected in series" between an'input terminal and'acorresponding output terminal. A'third condenser C2 forms the shunt impedance and is connected between the common terminal of'the conde'nsersci and the other side of the filter. The inductance 'unit T comprises two windings having self inductances equal in value,. respectively, to L and 2L, coupled by a mutual inductance M equal in value to L. The two windings have acommon terminal 12 and'are connected in series opposing relation with respect to their other two terminals .lland 13; thatis, they are so connected that fluxproduced by the current in one winding'is opposed'or decreased by the current flowing in the other winding. The Winding of value 2L is connected in parallel. with the two condensers C1 between their outer terminals, and the other winding L is connected in parallel with one'only of the condensers C1.

The presence of the mutual inductance be tween the two windings of the inductance unit is equivalent to the insertion of an additional self inductance of value M in a branch common to the two coil windings. Fig. 2 shows 'a circuit which is electrically equivalent to the oneshown in Fig. 1. By equivalence of-networks, as the term is here used, is meant thatone network may be substituted for the other in any system without affecting the current and voltage relations in any other part of theisystem. In Fig. 2 the twowinding inductance unit has beenreplaced by its equivalent T-network of three separateinductance's, A, Band M, the'values of which are.

The ooilterminals 11, 12 and 13 represent the same points in the network of Fig. 2 as they do,

in that of Fig. 1. As shown by Equations (1), (2) and- (3) with the values assigned to the two coil windings and theimu'tualinductance inFig. l

the B-arm of the equivalent T-network of Fig.

35 akstrap having zero impedance; The filter one double-winding'coil is made to take the place of two individual inductance coils.

Another filter section embodying the invention is shown schematically in Fig. 4, in which there are two inductance units Ti andTz. The unitTi has two windings with self inductances equal, respectively, to L2 and to L1 plusLz, coupled by mutual inductance M1 equal in value to L2. The

self inductances of the two windings of Tzare equal, respectively, toLs and to L1 plus L3, witha mutual M2 equal to L3 eifective'between the windings. T1 and T2 have their windingsconnected in the series opposing relation. A pair of equal capacitances C3 are connected in series. with the inductance units, and two more capacitances C4 and C5, form a part of theshunt impedance of the filter. By replacing the inductanceunits T1 and T2 by their equivalent T-networks, as was explained above in connection with Figs. 2 and 3, it is seen that the circuit of Fig. 4 is electrically equivalent to that shown by Fig.- 5, which. will be recognized as a band-pass filter section of the type described in U. S. Patent 1,644,004, issued October 4, 1927, to 0.,J. Zobe'l. Each of the inductance units T1 and T2 may consistof two windings placed upona single core and potted in a single coil case. 'Thus, two-coils serve to provide the equivalent of four separate inductances L1, L1, L2 and L3, as shown in Fig. 5.

This invention isnot limited to the particular filter sections shown but may be greatly modi tied and applied to other varieties of wave transmission networks without departing; from the spirit of the invention, as defined in the append: ed claims. For example, other circuits such as series or parallel resonant circuits may be sub; stituted for the condensers ormay be connected in shunt to the inductances to give'other transmission characteristics.

. What is claimed is: s V

' 1. A wave transmission network comprising an inductance in series with respect to the direction of wave propagation and a second inductance in shunt thereto, said two inductances being so related as to have mutual inductance, saidtwo inductances being connected in series opposing re lation, said mutual inductance being ,equal in magnitude to saidshunt inductance, and said in-. ductances eiiectively adding a third inductance in series with said series inductance while reducing the effective impedance of @said shunt inductance substantially to zero.

2. An electrical network adapted to be connected between two sections: of a circuit, said network comprising a series inductance and a shunt inductance, said two inductances being so related as to have mutual inductance and being connected inrseries opposing relation, the value of said mutual inductance being'equal to the self inductance of one of saidinductances,saidpin ductances efiectively adding anotherinductance in series with said" series inductance, -and said "added inductance cooperating with the other ele ments' of said network'to produce a transmission 1,970,933 i f f l band in the attenuation characteristic of said network.

3. A Wave filter section comprising a plurality of circuit branches disposed in series and shunt relationship with respect to the direction of wave propagation, reactive impedances associated in said branches, an inductance included in one of said series branches and a second inductance included in an adjacent shunt branch, said two inductances being so related as to have mutual inductance therebetween and being connected in series opposing relation, the value of said mutual inductance being equal to the self inductance of one of said inductances, said inductances effectively adding an inductance element to one .oilsaidseries branches, the impedance of said element cooperating to permit the filter to pass freely a band of frequencies while attenuating other frequencies.

4. Awave transmission network having a pair of input terminals anda pair of output terminals, said network comprising electrical paths. between each input terminal and a respectively associated output terminal, two impedances ,included in series in one of said paths, an'induc; tance connected in parallel with said .two im-' pedances betweenthe outer terminals thereof, a second inductance connected in parallel with one of said two impedances, and athird imped ance connected between the junction'point of said two impedances'and apoint' in the other of saidpaths, said two inductances being so related as; to have mutual inductance therebetween, and the valve of saidmutual inductance beingequal to meet said two'inductancea I 5. A wave transmission network adapted to be connected between two sections of a circuit, said; network comprising a pair of capacitances connected; in series betw een the two sections, a third capacitance includedin a'shunt path hav{ ing one terminal connected to the junction point of said pair of capacitances, an inductance connectedin parallel with said pair of capacitances between-the outer terminals thereof, and a second inductance connected in parallel with one of said pair of capacitances, said two inductances being so relatedas to have mutual inductance and being connected in series opposing relation, the value ofsaid mutual inductance being equal to the selt inductance of said second inductance, said-inductances 'efiectivel'y adding an inductance element in series between the two sections of cir .cuit and-'nullifying the effect of said second inductance. I n j 6. An electric wave filter having a pair of input terminals and a pair of output terminals, saidnetwork comprising electricalpaths between each inputterminaland arespectively associated output terminal, two capacitances included in series in one of; saidpaths, an inductance connected'inparal-lel with said two capacitances be tween the outer terminals thereof, a second in? ductance connected in parallel with one of said two capacitances, and a third capacitance connected between the junction point of said ,two

capacitances. and a point in the other of said paths, said two inductances being so relatedas .to chave; mutual inductance and being connected in series opposing relation, the value of said mutual inductaneexbeing equal to the self inductance of one of said-inductances.

. I 7. A wave filter section comprising a plurality .ef circuit branches disposed in series and shunt relationship with respect to the direction of wave .plfopagation, yreactive impedances associatedin said branches, said impedances incuding a pair of coupled inductances included in two of said series branches which are separated by a shunt branch, said inductances effectively adding an inductance element to said shunt branch while at the same time annulling the effect of one of said pair of inductances, the impedance of said added inductance element cooperating to permit the filter to pass freely a band of frequencies While attenuating other frequencies.

8. A wave transmission network comprising a plurality of circuit branches arranged in series and shunt relationship to the direction of wave propagation, a reactive impedance in a shunt branch and two inductances included in two of said series branches which are separated by said shunt branch, said two inductances being so related as to have mutual inductance and being connected in series opposing relation, the value of said mutual inductance being equal to the self inductance of one of said two inductances, said inductances effectively adding an inductance elereactive impedance, means for connecting said reactive impedance between two sections of a circuit and an inductance connected in series between said impedance and each of the two sectlons, said inductances being so related as to have mutual inductance and being connected in series opposing relation, the value of said mutual inductance being equal to the self inductance of one of said inductances, whereby an inductance element is effectively added to said reactive impedance and the effect of one of said series inductances is annulled. I

'10 A wave filter adapted to be connected between two sections of a circuit, saidvfilter comprising a shunt impedance and an inductance at each side of said impedance, said inductances being so related as to have mutual inductance and being connected in series opposing relation, the value of said mutual inductance being equal to the self inductance of one of said two inductances, said inductances efiectively'adding aninductance element in said shunt impedance while at the same time annulling the effect of one of said two inductances, the impedance of said added inductance element cooperating to permit the filter to pass freely a band of frequencies while attenuating other frequencies.

' CARL L. FREDERICK. 

